The beauty or attractiveness of gemstones, and in particular diamonds, is considered to be directly related to how the stones interact with light. This interaction is known as the “play of light” and incorporates properties such as brilliance, fire and scintillation displayed by the stone. Brilliance relates to the intensity and contrast of light returned by the stone to the observer, fire relates to the amount of dispersed light returned by the stone and scintillation relates to the incidence of light flashes visible to the observer as the stone is moved relative to a light source.
Recently the practice of marking gemstones with brand marks, identification numbers, and/or marks conveying other information regarding the gemstone has become more widespread. Marks may be applied to stones using a variety of methods, such as for example those described in WO 98/52774. The marks can be applied in such a way as to be invisible to the eye using a ×10 loupe so that they do not detract from the value or appearance of the gemstone. This means that the marks can be applied to facets such as the table of the stone. Such marks are typically inscribed to a depth of up to about 0.05 μm into the stone.
In the retail environment it would be advantageous to provide a quick, practical and effective viewer that would allow a retailer to display to a customer both the play of light in a gemstone and the inscribed mark.
There are a number of viewers currently available that can be used to view play of light in gemstones. One example of such a viewer is provided in WO 2001/14854. Further viewers can also be used to view marks inscribed in stones, and such a device is described in WO 99/34197 which provides means to view a magnified image of the gemstone and the mark, but does not provide a means of viewing the play of light in the stone. A further viewer is described in EP 1319942 which enables the display of both play of light and a mark. However, due to the difficulty in providing the correct lighting conditions to display the play of light and the mark, the gemstone must be moved from one part of the viewer to another to view these different attributes.
It is known that, in order to display the properties of brilliance, fire and scintillation, varied lighting conditions are required. For example, the level of dispersed light may be hidden by the high level of reflected white light of a very brilliant gemstone under some lighting conditions. Varied lighting conditions may be provided by movable annular lighting such as that employed in the BrillianceScope™ Analyzer that measures the light that is returned through the crown of a diamond when it is illuminated from 6 different angles in a controlled lighting environment. It has also been shown to be advantageous to use multiple directional light sources, such as that produced by a number of LEDs, particularly when displaying the fire and scintillation of a gemstone. EP 1319942 describes an apparatus for determining play of light of a gemstone using a highly symmetrical lighting pattern that can be rotated and whose intensity can be controlled to vary the lighting. This symmetrical lighting system emphasises the symmetry of the stone. However, it is also known that, although highly symmetrically cut stones provide a good predictability for good play of light, stones with a lesser degree of symmetry can give equally good play of light.
Similarly, U.S. Pat. No. 7,315,356 provides an apparatus for imaging the fire of a gemstone where the varied lighting is provided by a symmetrical lighting pattern. It has been found that using a highly symmetrical lighting pattern does not provide adequate means for visual appreciation of the play of light for the majority of stones.
The present invention aims to overcome or at least alleviate one or more of the difficulties associated with the prior art.